The polyamines, putrescine, spermidine, and spermine, are major polybasic compounds in all living cells. These amines have been shown to be important for many systems related to growth and differentiation. We have been interested in how these polyamines are synthesized, how their biosynthesis and degradation are regulated, their physiologic functions, how they act in vivo, and in characterizing the structure of the various biosynthetic enzymes. For this purpose we have constructed null mutants in each of the biosynthetic steps in both Escherichia coli and in Saccharomyces cerevisiae, and have prepared overexpression systems for the biosynthetic enzymes. Our present studies are directed at extending our studies on the biochemistry, regulation and genetics of these amines and of the biosynthetic enzymes in S. cerevisiae. During the current year we have continued our studies on the regulation of the enzyme ornithine decarboxylase which is a key enzyme in the formation of the polyamines, and is of special interest in studies on the physiological function of the polyamines. The ornithine decarboxylase levels are markedly lowered after the addition of spermidine to the medium, both by repression of new synthesis and by degradation of the existing enzyme. We have found that, contrary to previous reports in the literature, an important part of this degradation involves the induction of a proteolytic activity. This induction does not occur if protein synthesis is inhibited. Using overexpression systems in E. coli, we have developed methods for the isolation of large quantities of purified yeast ornithine decarboxylase, S-adenosylmethionine decarboxylase, spermidine synthase and spermine synthase for crystallographic and other structural studies. The structure of S-adenosylmethionine decarboxylase is of particular interest since it is formed as a proenzyme and is post- translationally cleaved to from a pyruvoyl group that is essential for enzymatic activity. We have also cloned (with PCR technology) the E. coli gene for glutathionylspermidine synthase as the initial phase of a study of the function of this compound in E. coli. - putrescine, spermidine, spermine, yeast, polyamines. ornithine decarboxylase, S- adenosylmethionine decarboxylase